The long-term objectives of the proposed research are: (1) to learn more about human ocular motor disorders that impair the vision necessary for everyday activities, and (2) to appraise therapeutic measures to restore clear vision. The research strategies are to relate reliable measurements of eye movements to visual complaints of patients doing natural behaviors; and to use measurements of normal and abnormal eye movements to test mathematical models that are biologically plausible; and evaluate new treatments of disorders of ocular motility using controlled trials. There are five specific aims, which grow out of prior studies: The first project comprises tests of models for acquired pendular nystagmus. Determination of the effects of large gaze shifts and luminance changes will be used to test control systems and neural network models. The second project aims to determine whether eye movements prior to head rotation improve the gain of the vestibulo-ocular reflex, during sudden head turns. This "priming" effect may occur with a variety of prior eye movements but not in patients with a deficient gaze-holding mechanism (neural integrator). The third project aims to test whether Hering's law applies to saccadic pulses (i.e., equal pulse size) during disjunctive gaze shifts. Normal subjects and patients with internuclear ophthalmoplegia will be studied. The fourth project comprises tests of models that account for saccadic oscillations. Using a new experimental technique to induce saccadic oscillations in normal subjects and patients, the effects of cerebellar and brainstem lesions will be systematically investigated. The fifth project is a controlled evaluation of scopolamine and gabapentin as treatment for acquired forms of nystagmus. It has been shown that gabapentin suppresses pendular nystagmus, but side-effects such as ataxia limit the dosage tolerated. Scopolamine may prove more effective in patients with oculopalatel tremor. In sum, these projects will prove new information on the pathogenesis and treatment of a range of common disorders of eye movements that disrupt clear vision.